Extremophiles
Organisms that thrive in extreme or harsh environments are known as extremophiles. Harsh conditions can include very high or very low temperatures, unusually dry or salty environments, acidic or alkaline conditions, high pressures, or environments with gases that are toxic to many animals and plants, such as hydrogen sulfide or carbon monoxide.

Regulation of Gene Expression
The chromosomes of every type of cell carry two major kinds of genetic information: DNA sequences that ultimately specify the amino acid sequence of proteins, and sequences that regulate the expression of those protein-coding sequences. Since DNA is first transcribed into RNA sequences, and then some of these RNA sequences are translated into proteins, cells control the expression of their genes at several levels, including the rate at which specific RNA sequences are made, the ways in which those RNA sequences are modified, the rate at which modified RNA sequences are translated into protein chains, and the changes that occur during and after protein chains are synthesized, which includes such changes as folding, protein degradation, and chemical modifications, such as the addition of phosphate groups for example. Regulation depends on complex networks of receptors, signals, and enzymes that allow cells to adapt to the requirements of life in particular environments.